Heretofore, various heat transfer techniques have been known in the art, including sublimation type transfer systems wherein a sublimable dye is carried on a substrate sheet such as paper to make a heat transfer sheet, which is then overlaid on an imageable material (image-receiving material), for instance, a woven fabric made of polyester to apply heat energy in the form of a pattern from the back side of the heat transfer sheet, thereby transferring the sublimable dye into the imageable material.
With a sublimation textile printing system of the above sublimation transfer systems, in which the imageable material used is made of, e.g., a polyester textile, relatively satisfactory dye transfer is achieved, since heat energy is applied over a relatively extended period of time so that the imageable material per se can be heated by that heat energy.
With an advance in recording techniques, however, fine characters or figures or photographic images could have been formed at high speeds on imageable materials made of, e.g., polyester or paper sheets having thereon a dye-receiving layer by means of a thermal head, etc. In this case, the application of thermal energy is required to be achieved within a time as short as fractions of a second. However, no image of sufficient density can be obtained, since the sublimable dyes and imageable materials are not well heated within such a short time.
In order to cope with such high-speed recording, sublimable dyes excelling in sublimability have thus been developed. However, problems with such dyes of excellent sublimability are that after transfer, they transfer into the imageable materials or bleed onto their surfaces with time, generally because of their low molecular weight. In consequence, the images, once formed, become out of order or blurred, or otherwise contaminate surrounding articles.
In the art of heat transfer using sublimable dyes, there is thus still strong demand for the development of a heat transfer sheet which provides a clear image of sufficient density by the application of thermal energy within such short a time as mentioned above and imparts improved fastness properties to the formed image.
It is therefore an object of the present invention to satisfy the above demand.